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A Stopwatch instance can measure elapsed time for one interval, or the total of elapsed time across multiple intervals. In a typical Stopwatch scenario, you call the Start method, then eventually call the Stop method, and then you check elapsed time using the Elapsed property.

A Stopwatch instance is either running or stopped; use IsRunning to determine the current state of a Stopwatch. Use Start to begin measuring elapsed time; use Stop to stop measuring elapsed time. Query the elapsed time value through the properties Elapsed, ElapsedMilliseconds, or ElapsedTicks. You can query the elapsed time properties while the instance is running or stopped. The elapsed time properties steadily increase while the Stopwatch is running; they remain constant when the instance is stopped.

By default, the elapsed time value of a Stopwatch instance equals the total of all measured time intervals. Each call to Start begins counting at the cumulative elapsed time; each call to Stop ends the current interval measurement and freezes the cumulative elapsed time value. Use the Reset method to clear the cumulative elapsed time in an existing Stopwatch instance.

The Stopwatch measures elapsed time by counting timer ticks in the underlying timer mechanism. If the installed hardware and operating system support a high-resolution performance counter, then the Stopwatch class uses that counter to measure elapsed time. Otherwise, the Stopwatch class uses the system timer to measure elapsed time. Use the Frequency and IsHighResolution fields to determine the precision and resolution of the Stopwatch timing implementation.

The Stopwatch class assists the manipulation of timing-related performance counters within managed code. Specifically, the Frequency field and GetTimestamp method can be used in place of the unmanaged Win32 APIs QueryPerformanceFrequency and QueryPerformanceCounter.

Note

On a multiprocessor computer, it does not matter which processor the thread runs on. However, because of bugs in the BIOS or the Hardware Abstraction Layer (HAL), you can get different timing results on different processors. To specify processor affinity for a thread, use the ProcessThread.ProcessorAffinity method.